virsh: Fix XPATH in virshDomainDeviceAliasCompleter()
virsh: Fix XPATH in virshDomainDeviceAliasCompleter()

The way this completer works is that it dumps XML of specified
domain and then tries to look for @name attribute of <alias/>
element. However, the XPATH it uses is not correct which results
in no aliases returned by the completer.

Signed-off-by: Michal Privoznik <83d82aaba2eed257f4814b0c239c260c4caaadf0@redhat.com>
Reviewed-by: Peter Krempa <2cf5c04c61aa466e4a47bfedc747d17279c72ffc@redhat.com>

nertpinx/libvirt,crobinso/libvirt,olafhering/libvirt,crobinso/libvirt,libvirt/libvirt,olafhering/libvirt,nertpinx/libvirt,libvirt/libvirt,jfehlig/libvirt,libvirt/libvirt,libvirt/libvirt,olafhering/libvirt,zippy2/libvirt,jfehlig/libvirt,olafhering/libvirt,zippy2/libvirt,crobinso/libvirt,nertpinx/libvirt,nertpinx/libvirt,zippy2/libvirt,crobinso/libvirt,jfehlig/libvirt,zippy2/libvirt,jfehlig/libvirt,nertpinx/libvirt